1. Field of the Invention
The present invention relates to a solid oxide fuel cell (SOFC) which uses a solid electrolyte to obtain electric energy by utilization of electrochemical reactions.
2. Description of the Related Art
Fuel cells have recently attracted considerable attention as a clean energy source which is capable of high energy conversion and globally environmentally friendly.
A solid oxide fuel cell (hereinafter referred to as “SOFC”) is one having a structure in which two electrodes consisting of an air electrode (cathode) and a fuel electrode (anode) sandwich a solid oxide electrolyte layer. Reactive gas containing oxygen is supplied to the air electrode, and reactive gas containing fuel gas is supplied to the fuel electrode. An electrochemical reaction occurs at a three-phase interface where the electrode, the reactive gas and the solid electrolyte mainly contact. These electrode materials are required to offer the following properties 1) to 3).
1) To promote the electrochemical reaction at the electrode/electrolyte interface (i.e. the interface between the electrode and the electrolyte), the electrode materials have a structure which can obtain a large area of the three-phase interface formed by the electrode material, the electrolyte and the reactive gas.
2) The electrode materials have a structure which makes it easier to introduce the reactive gas into the electrode/electrolyte interface that is an electrochemical reaction field.
3) The electrode materials offer low electric resistance to enhance electricity collecting performance as the electrode.
To satisfy the properties of the items 1) and 2), the electrode must be porous, and to decrease its electric resistance, the electrode layer must have a sufficient thickness.
Accordingly, in order to offer the above described properties of the 1) to 3), with respect to the conventional electrode material, its micro powders were processed to be pasty, and coated onto the surface of the electrolyte layer by use of a printing method and a dipping method, followed by baking. Thus, the fuel electrode and the air electrode, which are a porous single-layer having a sufficient thickness, are respectively formed.